Monoclonal antibodies reactive to cell surface antigens of LT teratocarcinoma stem cells are being used as reagents to study the cell surface molecules present on developing embryos and to identify molecules involved in cell-cell recognition of teratocarcinoma embryonal cells and normal murine cells. LT teratocarcinoma embryonal cells form tumors exclusively in the gonads of many female mice. This specificity was shown to be not due to selectively localized growth factors, since tumor growth occurs in many directly injected tissue sites in normal and castrated animals of both sexes. The site-specificity correlates with selective cell adhesion to cells of the target organ. 125IUDR-labeled cell-tracing studies and tumor growth patterns following intraperitoneal and intracardial injection of tumor cells indicate that cells effectively enter the organ via the peritoneal space. Preferential binding, previously shown to occur to fetal ovary monolayers, was demonstrated to occur to whole adult ovaries also, both in vivo and in vitro. These results indicate that the ovarian germinal epithelium is the cell type of the whole organ responsible for the selectivity of the initial adhesion step. Monoclonal antibodies purified by affinity chromatography are being tested for their ability to block adhesion between embryonal carcinoma and germinal epithelial cells. This recognition, which results in site-specific tumor growth, is postulated to be derived from the embryonic migratory behavior of the normal cell of origin--in the case of the LT embryonal cell, the normal germ cell. It is the long-term objective of our studies to identify and biochemically characterize molecules important in early embryonic recognition events. The identification of molecules involved in specific recognitions of teratocarcinoma embryonal cells may be used to investigate the mechanisms tumor cells use to successfully metastasize.